Metal core substrates are produced as follows. On each of a top surface and a bottom surface of a core plate having predetermined holes, an insulating layer and a copper foil are sequentially stacked in this order from the inner side to form an integrated copper-lined stacking substrate. The copper-lined stacking substrate is put to a production line. In the production line, the copper-lined stacking substrate (work), for example, have through-holes formed therein, is plated and is patterned. As a result, a plurality of products are formed on one work (namely, a plurality of metal core substrates, namely, a plurality of metal core printed wiring boards each having a wiring pattern are formed on one copper-lined stacking substrate). Such products are separated from each other by outline shaping, and subjected to predetermined inspections and the like. Thus, production of the metal core substrates is finished.
By outline shaping, the integrated plate including the stacked core plate and insulating layers is cut into the plurality of products. Therefore, as shown in FIG. 8, the insulating layers 101 and the core plate 102 included in each metal core substrate 103 are exposed along the entirety of an end surface of the metal core substrate 103.
Therefore, when the end surface is wetted by moisture, dew or the like, the insulating property between a wiring pattern 104 in a top layer of the metal core substrate 103 and the end surface of the core plate may possibly be deteriorated. In order to avoid this, especially when the inner layer is to be used as an electric wire, a measure against migration needs to be provided.
Outline shaping is performed to cut the core plate and thus has an inconvenience that burr or shear drop is caused. A reason for this is that outline shaping is commonly performed by die machining.
Another technique for outline shaping is routing. By routing, a drill-like circular bit including a blade on a side surface thereof cuts a member to be processed in a manner like tracing an end surface thereof. Therefore, routing has a disadvantage of being unable to perform a large amount of processing in a short time. By contrast, die machining, which is a method of punching out a member by use of a die and a punch, has an advantage of having a high productivity and thus is often used.
However, as shown in FIG. 9, an end surface of the metal core substrate processed by outline shaping, more specifically, die machining has shear drop 105, sheared face 106, broken face 107, and burr 108 although the degree thereof varies.
As the burr is larger, the insulating property is more deteriorated. When shear drop is caused, the core plate 102 and the insulating layer 101 are peeled from each other at the shear drop. When the core plate 102 and the insulating layer 101 are excessively peeled, delamination may be caused.
Patent Document 1 discloses a technique proposed to solve such inconveniences. According to this technique, before outline shaping is performed, a metal plate of a part that is to be subjected to outline shaping is removed by etching, so that only the resin part stacked on the metal plate is punched out. This is devised to prevent the quality of the post-processing product from lowering by burr. Since the metal plate is not punched out, burr or shear drop is not caused.
However, such a technique needs an increased number of steps and thus complicates the work, and in addition, cannot be used to produce a metal core substrate including a resin portion at each of two surfaces of the core plate.
Referring to FIG. 10, when die machining is used for outline shaping, relatively large processing margins X and Y need to be provided. FIG. 10 is a plan view of the core plate 102 in the case where four products, namely, four metal core substrates, are to be produced from one work. Rectangular parts enclosed by phantom lines (phantom outline shaping lines 109) are to be the metal core substrates. When die machining is used for outline shaping, the processing margins X and Y each need to have a size of about 5 mm. This may cause a problem of limiting the number of products which can be produced from one work.